A no-nonsense woman named Jenny Edwards runs Help for Horses, an organisation in Washington state, USA, that nurses abused and abandoned equines. After the police, she, along with the father and brother of the deceased, was first to arrive at a farm in the small town of Enumclaw after the demise of a 45-year-old man on July 2 2005. Known to the public only as Mr Hands, his internet handle, he died, according to the coroner's report, from "acute peritonitis ... perforation of the sigmoid colon by a horse". Like others in this bucolic farming region, and in the city of Seattle, an hour's drive away, Edwards was appalled at the discovery of a community of "zoos", or zoophiles - people with a sexual attraction to other species - in the town.

By the end of Zoo, Robinson Devor's film about the zoos and the death of Mr Hands, Edwards has had a change of heart. Remarkably, she comes to believe that her own relationship to horses (we see her spending the night, platonically, among them in the fields) is not so far from those of the zoos. She acknowledges "the love and care they give their animal partners" - comparing that with what "normal" people do to animals, from spaying and gelding, to hunting them for sport and experimenting on them in the name of science - then adds: "I'm right at the edge of being able to understand it."

Cannes has had its fair share of sensations over the years, but Zoo, screening during the Director's Fortnight, looks set to be one of the most controversial films ever shown at the festival. Devor is as much an advocate for the rights of the zoos as Edwards is for those of horses. He and his co-writer, Charles Mudede, a cultural critic and journalist, saw an opportunity to address what they consider "the last taboo", by providing a context in which to give the zoos back their humanity and destigmatise their sexual preference.

Devor decided that a highly stylised approach would be the most effective to counter the widespread dismissal of these men and their orientation. Anyone seeking titillation will be disappointed. "I aestheticised the sleaze out of it," says Devor. You could blink and miss the well-circulated, grainy, explicit clip of Mr Hands being penetrated by an Arabian stallion, taken from the numerous videotapes he and his fellow zoos shot of one another; the camera pans around detectives and the relatives of one zoo, assembled to watch the scene on a monitor. Devor says he was influenced not by other documentaries but by highly stylised fiction films: Andrei Tarkovsky's The Mirror, Wong Kar-Wai's Happy Together, and Alain Resnais's Hiroshima, Mon Amour.

In part, his artistic choices are a result of limitations. The family of Mr Hands - a divorced father outed in the Seattle media as Boeing engineer Kenneth Pinyan, although never named in the film - refused to participate. Only one zoo, known as Coyote, agreed to appear on camera. The two other main characters would only record on audiotape. Devor recreated the essence of the zoo lifestyle with actors, adding haunting music, and he avoided a linear narrative, with its expectations of cause and effect.

The zoos and Devor believe that sex with horses is consensual. We see the zoos engage in affectionate foreplay, the building of trust between man and animal. One zoo claims Mr Hands perished because he and the man who aided him had not built a trusting relationship with the animal. Others in Washington disagreed. Led by Republican state senator Pam Roach, outraged rightwing politicians, religious leaders and animal rights organisations argued that horses do not have the cognitive ability to choose whether or not to participate in sex with a human. "Studies have shown a strong link between sex with animals and paedophilia," said Daniel Satterberg, a deputy prosecutor, in support of Roach's successful bid to introduce anti-bestiality legislation. However, the law was passed too late to convict the zoos, with the exception of one man, known as H, who was charged with trespassing.

Oddly enough, ultraconservative radio commentator Rush Limbaugh sided with the zoos. In the film, we hear his voice during a broadcast, asking: "Can it be disputed, given the evidence, that the horse was a willing participant?"

Whatever sense of community the zoos had was shattered when the scandal erupted. Each is shown alone, looking lost. "We always divided the film into two: paradise and paradise lost," Devor explains.

Although the subject matter is the stuff of sensationalist headlines, the decision to forgo a talking-heads documentary in favour of high-end tableaux seems to position the film for the arthouse. Still, Zoo is not devoid of humour, intentional or otherwise, with some characters' statements begging to be laughed at. "We were friends for all these years," says H, decrying the shunning he received when his secret life came to light. "And now all of a sudden I'm no good because I love the horse?"